The present invention relates to a multi-shaft driving apparatus and a fluid rotary apparatus.
Conventionally, equipment is provided with multi-shaft driving apparatus for driving a plurality of shafts synchronously by a plurality of motors.
In order for the multi-shaft driving apparatus to rotate a plurality of shafts synchronously with a high accuracy, it is proposed that an encoder, a pulse generator, and a motor control circuit are provided for each motor. The encoder detects the rotational state of each. The pulse generator generates pulse signals for rotating the shafts. The motor control circuit, having a PLL control section, inputs the pulse signals outputted from the pulse generator and pulse signals fed back by the encoder as a result of the detection of the rotational states of each shaft. In the above construction, a PLL control loop which passes through the PLL control section is formed.
According to the above multi-shaft driving apparatus, the shafts are driven synchronously in a steady state by the PLL control section, but they do not rotate synchronously during transient states such as rise time and fall time in the rotations of the shafts because PLL control is not performed during such transient states.
Vacuum technology is used in a very wide range from a technological field closely relating to daily life to a high technological field. Thus, vacuum technology is indispensable for technological progress.
Recently, an oil-free dry pump which forms a clean vacuum has become noteworthy in view of the progress of semiconductor industry.
The dry pumps now used includes screw type, scroll type, and claw type pumps. A positive-displacement vacuum pump is normally used in a low vacuum degree ranging from atmospheric pressure to 10.sup.-2 -10.sup.-3 torr. The positive-displacement vacuum pump comprises a plurality of rotors accommodated in a housing; a plurality of driving shafts which rotate the rotors synchronously; and a fluid suction opening and a fluid discharge opening formed in the housing. Utilizing the volume change of a space formed by the rotors or by the housing and the rotors, the drive pump draws and discharges fluid.
In order to make the pump oil-free, the conventional pump comprises a timing gear for rotating a motor shaft for driving synchronously a plurality of rotors; an oil chamber provided in a space accommodating a bearing; and a mechanical seal provided between the oil chamber and a space (suction chamber) formed by the rotors and the housing so as to prevent oil from penetrating into the space.
However, according to the conventional pump of the above construction, it is necessary to periodically replace oil and the mechanical seals and in addition, it is difficult to prevent the leakage of oil from the oil chamber.
The inventors of the present invention have already proposed a fluid rotary apparatus (oil-free vacuum pump) comprising two rotors synchronously rotated without contacting each other by the above-described multi-shaft synchronous control. However, the proposal does not describe the method for synchronously rotating the rotors during the starting and stopping of the vacuum pump.